Pediatric mechanical circulatory support is a critical unmet need in the United States. Each year, scores of children with end-stage heart failure die waiting for a heart transplant before a suitable donor heart can be identified. Extracorporeal membrane oxygenation (ECMO), the standard of care for pediatric mechanical support in the U.S., is not capable of providing the kind of long-term or chronic circulatory support necessary for children awaiting heart transplant (i.e., weeks to months). Recently, the Berlin Heart EXCOR(r) Pediatric Ventricular Assist Device (VAD) has emerged as a potential alternative to ECMO for children requiring mechanical assist as a bridge to heart transplant. The Berlin Heart is a miniaturized paracorporeal pneumatically-driven displacement blood pump similar in design to adult ventricular assist devices which appears capable of providing chronic mechanical circulatory support to children as small as 3 kilograms for up to a year or more. Preliminary data from Europe and North America suggest that two-thirds of patients can be bridged successfully to transplant using the device. However, detailed safety information-especially with respect to the most feared complications of stroke and thromboembolism-has been insufficient thus far to meet the FDA's quality standards for regulatory approval in children. The specific aim of this multicenter single-arm prospective clinical trial is to formally evaluate the safety and efficacy profile of the Berlin Heart EXCOR Pediatric VAD as a bridge to heart transplant in children with severe heart failure to facilitate FDA approval of the device under the Humanitarian Device Exemption (HDE) regulation. The primary efficacy endpoint of this clinical trial is waitlist survival to transplant or recovery;the primary safety endpoint is the proportion of patients developing a critical adverse event using standardized definitions adapted from the National Heart Lung and Blood Institute's INTERMACS project. The primary purpose of the study is to improve waitlist survival among children awaiting heart transplantation in the U.S. In addition, it is also hoped that the broader pediatric cardiology community can draw important lessons from this first device trial experience in pediatric mechanical support to benefit the design of future device trials in pediatric mechanical circulatory support.